Method of preparing electric discharge devices



E. E. CHARLTON 1,738,420

METHOD OF PREPARING ELECTRIC DISCHARGE DEVICES Filed March 26, 1926 Invennor:

His Attorney.

Patented Dec. 3, 1929 ,UNITE. STATES PATENT FFl ERNEST E. CHARLTON, OF SCHENECTADY, NEW YORK,- ASSIGNOR T0 GENERAL ELEC- TRIC COMPANY, A CORPORATION OF NEW YORK METHOD OF PREPARING ELECTRIC DISCHARGE DEVICES Application filed March 26, 1926. Serial No. 97,717.

The present application is a part continuation of application, Serial No. 608,311, filed December 21, 1922, which is in turn a part continuation of application, Serial No. 588,- 074, filed September 13, 1922.

My, present invention relates to the mtroduction of highly oxidizable materials into electric discharge devices and its .pbject is to provide such'devices with desird charges of highl reactive metals, such as the members of t e alkali group, without the difficulties and wastefulness entailed by former practice.

Heretoiore great dificulty has been experienced in introducing sodium and potassium in a clean, unoxidized condition into electric discharge tubes. A great part of this difficulty is due to, the marked chemical activity of these metals with many gases and vapors,for example, air and water vapor which unavoidably come into contact there- I with. Repeated wasteful distillation of these metals through along series of containers was required in order to free the metal from oxides, hydroxide and other impurities. Even :greater'ditficulties were encountered in v the introduction er the metals'oeesium and rubidium which have a very much higher vapor pressure than sodium 101: potassium, and are more active chemically. In fact, in the case of these latter metals these {difficulties would prohibit the practical use of these metals in discharge devices.

In accordance with my invention highly reactive materials, such as the alakli metals, are introduced into vacuum tubes, or other discharge devices, direct from a reaction mixture, that is, without permitting the reduced metal to come into contact with the air or other chemically active medium. The mixture may be placed either within the device itself or in a side chamber communicating directly with the vacuousspace within the discharge device. This procedure permits of removal of undesired gases from the device preceding the reduction of the desired metal from its compound in the gas-freed space, and of removal of whatever gases may be produced during reaction.

The accompanying drawing shows in Fig.

1 an electric discharge device charged with a rare gas and provided with an auxiliary chamber containing a reaction mixture; Figs. 2 and 3 show devices in which a reaction mixture has been provided on the electrodes; Fig. 4 illustrates a device in which a capsule for the reaction mixture has been provided in the device, this container being mounted directly on an electrode; Fig. 5 illustrates a modification (the bulb and other parts being omitted) in which a charge of reaction mixture is provided in a capsule capable of being heated independently of the electrode, and Fig. 6 illustrates a specific form of holder or capsule for the reaction mixture.

Referring to the drawing, the device shown for illustrative purposes in Fig. 1, comprises a gas lamp consisting of a glass container 1,containing metal plate electrodes 2, 3 separated by a sheet of glass 4:. and connected as usual to sealed-in conductors 5, 6,. The wires 7 8 serve as anchors for the electrodes. A side tube 9 is connected to the bulb l by a glass tube 10, preferably in series with two distillation bulbs 11, 11', in which re-- duced alkali metal may accumulate.

I Before a reaction mixtureis introduced into the tube 9 the. apparatus is baked out at about 300 (3., andwhile heated the bulbs are exhausted by apparatus and methodsused in vacuum tube exhaust. taken to eliminate water vapor, that is, a liquid air trap or similar device is provided between the exhaust tube 12 and the pump (not shown). When "the apparatus has cooled to room temperature the chamber 9 is opened and the reaction mixture is placed therein. The reaction mixture, for example, may consist of a compound of an alkali metal, such as caesium chloride, and a reducing agent, preferably a material which produces non-volatile by-products, as for example, cal cium or magnesium. The latter reducing metals preferably are used as fine turnings and should be present in excess. The chamher 9 then is sealed and the whole apparatus is again heated while on the pump to 250 C. to eliminate moisture and other deleterious gas or vapor from the reaction charge, and also to again remove traces of gas taken up Particular care is which will evolve the desired alkali metal.

The alkali metal is then driven from thechamber 9 successively into the bulbs 11 and 11', and from thence into the main chamber 1, the vacuum pump preferably being operated continuously. The reduction bulb final ly may be sealed off from the main receptacle by fusion, as indicated by the dotted lines, or if desired, is permitted to remain attached during the operation of the device.

In the device shown in Fig. 1, a desired quantity of neon, or other fixed gas, may be introduced through a tube 13 (shown in dotted lines), connection to the pump through the tube 12 being shut off at that time. An excess of alkali metal has been indicated in the tube 1 at 14.

The gaseous glow lamp of Fig. 1 has been described for illustrative purposes only and it is to be understood that the introduction of.

caesium, or other alkali metal, into various other types of electron discharge devices may 1 be carried out in the same manner.

Fig. 2 shows a vacuum tube of the pliotron type comprising a filamentary cathode 15 and anode 16, and a grid or input electrode 17 contained within a sealed envelope 18 consisting of glass or other suitable material. These electrodes are connected to leading-in conductors sealed into a stem 19 and connected to a base 20 in the usual manner. The cathode may consist of pure tungsten, or of tungsten containing thoria, in accordance with Langmuir Patents Nos. 1,244,216 and 1,244,217. The container 18 commonly is baked out and exhausted to a high vacuum, but may in other cases contain a filling of attenuated gas, for example, argon.

Applied to some region of the device op- .erating at a high temperature, for example,

to the anode 16, is a small quantity 21 of a reaction mixture capable of evolving a desired alkali metal. For example, a mixture of a halogen compound of an alkali and alkaline earth metal may be applied with a suitable binder, such as a solution of a cellulose product in amyl acetate. When the anode is operated at an elevated temperature, for example, by high voltage bombardment with electrons or by means of a high frequency magnetic field (see Fig. 3), reaction occurs which evolves the desired alkali metal. Cacsium may be introduced in this manner to improve the operating characteristics of incandescent cathode devices. Of course, the alkali metal alsomay be introduced in a vacuum device as shown in Fig. 2 by the method described in connection with Fig. 1. It may also be introduced into electrical discharge devices, as-shown'in Fig. 2, by applying a part of the reaction mixture to the filament and the alkali metal being subsequently formed from the recreation mixture in situ by heating the filament to a suitable temperature by the passage of an electric current through it.

I have shown in Fig. 3 another type of enclosed or sealed discharge tube which in this case comprises a protective device for discharging high voltage. It contains disc electrodes 22, 23 consisting of aluminum or other suitable metal, and supported on wires 24, 25

which are sealed into the stem 26. The bulb 27 contains an inert or rare gas, as for example, neon, at a pressure within the range of several millimeters to several centimeters. Applied to one or both of the electrodes 22, 23, as indicated at 28, is a quantity of re action mixture capable of evolving alkali metal. The reaction is brought about in the presence or absence of the inert gas by heating the electrode in any suitable way, as for example, by means of a high frequency magnetic field induced by a winding 29 as primary, the secondary being constituted by the electrodes. Or the reaction may be brought about in the presence of an inert or rare gas. as for example, neon at low pressures by operating an electric discharge. This discharge in the gas between the electrodes is of a suitable current density which will heat the electrodes and reaction mixture sufficiently to evolve the alkali metal.

' As illustrated by Figs. 4 and 5 a reaction I mixture may be placed in a metal capsule 31, which is located within the bulb. In the form shown in Fig. 4 the capsule is mounted on the anode 32. As shown in Fig. 6 the capsule consists of a dished portion 33 and a plate 34 which may be closed over the dished portion as a cover and is held in place by the ears 35,

36. The reaction mixture, either in powder form or as a pressed pellet, is place-d within the capsule in a dry, gas-free state without a binder. The capsule is closed and then is mounted on the electrode 32 by spot welding as indicated. The tube thereupon is ,exhausted to a high vacuum. When the anode and capsule are heated, the pumping preferably being'continued, caesium vapor escapes through slits left between the cover and the capsule.

In the arrangement shown in Fig. 5 a slightly modified form of capsule 37 is mounted by a wire 38 in a position sufliciently re-.

moved from the anode 39 to permit of the anode and capsule being heated by high fre quency induction independently of one another. This capsule comprises a dished or cup-shaped member and a flat plate fastened to it at several points leaving crevices for the escape of vapor. It so happens that the capsule in the devices of both Figs. 4 and 5, has for the sake of convenience been connected to the anode. It is not essential to do this. The capsule may be supported in any convenient in the tube. The anode and related parts "evacuated to a pressure low enough to enable an electron discharge to be operated therein without gas ionization and lastly is charged with alkali metal by heating the capsule 37 by high frequency induction. Pumping preferably is continued during the reaction as traces of foreign gas are apt to be evolved even when a reaction mixture is chosen which produces solid by-products.

Although reaction mixtures such as a halide of the desired metal and an alkaline earth metal, are preferablefor the purpose of my invention, as very little gas is evolved incidentally during the reaction, the alkaline earth chlorides being non-gaseous, other reaction mixtures may be used. For example, the sulphate or silicate (CEBSllllIl-fillllfllllllll] silicate) may be used. A carbonate of a desired alkali metal may be used with calcium or magnesium as a reducing agent. Carbon dioxide is produced as one of the by-products,

.' but this gas is relatively inert and can be readily exhausted during the reaction. For some purposes reducing agents other than the alkaline earth metals, for example, even carbon may be used as the reducing agent. but its use is accompanied with greater difliculties.

The embodiment of my invention illustrated by Figs. 4, 5 and 6 are claimed in some of their specific aspects in a copending application Serial No. 49,164, filed August 10, 1912265, jointly by Dow O. Whelan and myse Although I have for illustrative purposes specifically referred to the introduction of caesium in electric discharge devices, I wish it to be understood that my invention may be embodied in devices charged with other reactive materials derived from their compounds by reduction in situ.

lVhen a device such as the three electrode pliotron shown in Fig. 4 is provided with a thoriated tungsten cathode and a quantity of caesium, an improved detector action is obtained as described in my copending application Serial No. 726,639, filed July 17, 1924.

What- I claim as new and desire to secure by Letters Patent of the United States, is,-

1. The method of providing a highly reactive material in an electrical discharge device, which consists in introducing said material by direct evolution from a reaction mixture capable of yielding the desired material unaccompanied by the evolution of gaseous by-products.

2. The method of introducing a highly reactive metal into an electric discharge device, which consists in placing within access of the discharge space in said device a compound of the metal to be introduced and a reducing agent evacuating said device and heating said materials to a reaction temperature to evolve said metal.

3. The method of introducing caesium into 7 an electron discharge device, which consists in freeing said device from undesired gas. introducing into said device a compound of caesium and an alkaline earth metal, heating said materials to a reaction temperature, removing dnring reaction gases incidentally produced and sealing said device.

4. The method of introducing an alkali metal into an electric discharge device without introducing gaseous by-products which consists inproviding therein in contact with one of the metal members of said device a mixture of a compound of said alkali metal and an alkaline earth metal, evacuating said device and heating said member to a temperature at which chemical reaction occurs accompanied by the evolution of the desired alkali metal.

5. The method of introducing an alkali metal into an electric discharge device which consists in providing within said device a mixture of the compound of the desired alkali metal and a reducing agent which will yield by the reduction of said compound alkali metal and inert by-products, heating said mixture toa reaction temperature, removing any gases which may be' evolved during the reaction and thereupon sealing said device.

6. The method of introducing an alkali metal into an evacuated electric discharge device which consists in providing within said device a mixture of the halide of an alkali and an alkaline earth metal and heating said mixture to a reaction temperature.

7 The method of introducing an alkali metal into an electrical discharge device without introducing deleterious gases which consists in applying upon a metal 'member in said device a mixture of a compound of said alkali metal and a reagent capable of reducing said compound unaccompanied by deleterious by-products, evacuating said device, and heating said member to a temperature sufiiciently high to cause reduction and volatilization of said alkali metal.

8. The method of introducing an alkali metal into an envelope containing one or more metal members which consists in applying a mixture of a halide of said metal and fragments of an alkaline earth metal upon a metal member in said device, producing in Cil eterious efi'ect upon the operation of said device and a mixture of a compound of a highly reactive metal desired in the completed form of said device and a reducing agent therefor'which yields said metal and non-gaseous products only when reacting with said compound, said mixture being located in communication with the discharge space.

10. An electric dischar e device containing a mixture of a halide of an alkali metal and an alkaline earth metal and means for heating said mixture to a reaction temperature.

11. An electric discharge device containing a mixture of a compound of an alkali metal and a reducing material and means for heating said mixture to a reaction temperature.

12. The combination of an electrical discharge device, a mixture of alkaline earth metal and a halide of an alkali metal therein and a member capable of being heated to a reaction temperature in heat-conveying relation to said mixture.

13. The electron discharge device comprising the combination of a sealed, evacuated envelope, a thermionic cathode, an anode, and a charge in said envelope comprising a mixture of a compound of an alkali metal and a reducing material and means for heating said mixture to a reaction temperature.

.14. An electric discharge device compris-" ing the combination of a sealed, evacuated envelope, a filamentary tungsten cathode, a plate-shaped anode and a grid, a mixture of a caesium compound and alkaline earth metal applied to one of said electrodes in a position where said mixture may be heated to a reaction temperature at which caesium is liberated.

15. The method of introducing a vacuum improving substance into an evacuated vessel comprising mixing a compound thereof with a reducing agent and a liquid binder, applying some of said mixture in said device and heating the same to cause a reaction and liberation of vacuum-improving material.

16. The method of introducing a clean-up material into an evacuated Vessel comprising mixing a substance containing the material in reducible form with a reducing agent, introducing the mixture into the vessel, and heating the mixture to cause a liberation of the desired clean-up material.

In witness whereof, I have hereunto set my hand this 25th day of March, 1926.

ERNEST E. CHARLTON. 

